Impact assessment of wetlands:

a framework for the UK Environment Agency

Mike AcremanCentre for Ecology and Hydrology

Wallingford, UK

Environmental impact assessment• EIA “… a means of drawing together, in a

systematic way, an assessment of a project's likely significant environmental effects”

• “... enables environmental factors to be given due weight, along with economic or social factors, when planning applications are being considered”

• EU Directive 97/11/EC • National legislation on EIA

European drivers for “water” EIAs• Habitats Directive (92/43/EEC) - conservation of natural habitats - wild fauna and flora- Special Areas of Conservation (SACs)- maintain at, or restore to, 'favourable conservation status'

• Birds Directive (79/409/EEC) - special measures to conserve the habitats of listed species - Special Protection Areas (SPAs).

• Water Framework Directive (2000/60/EC) - achieve ‘good status’ in all water bodies

UK specific drivers for “water” EIA

• Wildlife and Countryside Act 1981 • Environment Act 1995• Countryside and Rights of Way (CROW) Act

2000• Catchment Abstraction Management Strategies

(CAMs)• Catchment Flood Management Plans (CFMPs)

Almost 100 key wetlands to assessStaff not wetland experts

What drives the approach ?

Academics• Detailed understanding• Innovation• Intellectual challenge• Journal publications• Peer review

Agencies• Addressing legislation• Consistency• Fit for purpose• Cost effectiveness• Stakeholder

responsibility

Impact Assessment of Wetlands

Stage 1 Hydrological impacts assessment (abstraction on wetland hydrology)

Stage 2 Ecological impacts assessment (hydrology on wetland biota)

Stage 1 Hydrological impact assessment

• Level O- Conceptual understanding

• Level 1 Simple- Water balance

• Level 2 Intermediate- one layer (aquifer) drawdown estimates- Theis/Hantush/Neuman

• Level 3 Detailed- Distributed modelling- MODFLOW, ISIS, MIKE-SHE

What level of assessment?

• Risk-based approach• No right answer• Use simplest

approach that gives acceptable level of risk

• Move to higher level if results too uncertain

Model development

• Develop model• Test with data• Confirm or reject

conceptual understanding

develop

test

develop

test

Level 0 Conceptual understanding

Understanding how the wetland interacts with the surrounding hydrological system; atmosphere, aquifer unit or catchment

Water transfer mechanisms

• How water moves into and out of wetlands

• How wetlands interact with rivers, aquifers, lakes, the sea

• How landscape location influences water transfer mechanisms

Precipitation

Evaporation

Runoff

Outflow

Lateral inflow

Drainage

Overbank flow

Pumping

Spring flow

Groundwater discharge

Groundwater recharge

Groundwater seepage

Tidal inflow

Tidal outflow

Differing contact with the aquifer

Wetland landscape location

Flat area wetlands

Hill top

Low permeability layer

Slope wetlands

Spring-fed

Seepage-fed

Low permeability layer

Depression wetlands

Spring-fed

Groundwater discharge

Low permeability layer

Valley bottom

Spring-fed

Groundwater discharge

Low permeability layer

Underground

Coastal

Conceptual understanding

Pulfin bog, Yorkshire

Pulfin bog, Yorkshire

Level 1 Simple

• Water balance approach• Quantifying water transfer

mechanisms• Scenarios• Uncertainty

Water balance of wetlandsInputs to the wetland P: precipitation (rainfall, snow, dew etc)

directly on the wetland +R: surface and shallow subsurface inflow

to the wetland +L: lateral inflow +OB: over-bank inflow +PUi: water pumped into the wetland +S: spring flow +GD: groundwater discharge into the

wetland +GS: groundwater seepage into the wetland

Outputs from the wetland E: evaporation from the wetland +δV: change in volume of water stored within the wetland +D: drainage +OF: overland outflow +PUo: water pumped out of the wetlands +GR: groundwater recharge to aquifers +

where δV may be positive or negative

Sheringham Fen

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

P-E L

stream

GD

drift

GD

Chalk

OF

stream

Ml/d

Scenarios for Lopham and Redgrave Fen

-1.2

-0.8

-0.4

0

0.4

0.8

1.2

P-E

L riverL Little FenL M

iddleL Zone 1G

D C

halkD

riverD

Middle

D Little Fen

D Zone 1

GR

Chalk

Ml/d no abstraction

full licensed

Uncertainty in modelling• No measurement is exact • All data are uncertain • Need to assess the risk of being wrong • Define acceptable level of uncertainty• Improve data and models until “fit for purpose”

Sheringham Fen - uncertainty

-150

-100

-50

0

50

100

150

P-E R Brook GD drift GD Chalk OF Brook

% to

tal i

nput

Quantified conceptual understanding

Water quality• Wicken Fen drying

out?• Flooding from

groundwater fed river• Flood control• Dominance of rainfall• Change in pH• Driven by water

balance

Las Tablas de Daimiel 1960s

Las Tablas de Daimiel 1990s

Sheringham Fen - scenario

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

rain

inflow

evaporation

groundwater

outflow

Ml/d

long termcurrentdrought

Convert to water level

• Combine water balance model with specific yield of soil

• δs = SY δhwhere δs = change in storageSY = specific yield δh = change in water level -0.6

-0.5-0.4-0.3-0.2-0.1

00.10.20.3

1 2 3 4 5 6 7 8 9 10 11 12

month

wat

er ta

ble

leve

l

Level 2 Intermediate approach

• Soil physics/drainage equations• Hantush one layer leaky aquifer• Draw down levels• Rainfall-runoff model

Soil physics/drainage equations

H = f (DR, K, RH, R, E .. )

whereDR = distance from riverK = hydraulic conductivity

RH = river levelR = rainfallE = evaporation

-2

-1.5

-1

-0.5

0

0.5

0 20 40 60 80 100

distance from river

wat

er ta

ble

leve

lJanuaryAugustApril

Example simple assessmentHantush leaky aquifer model

Level 3 Detailed level

• Hantush gives 1-demensionl results – draw-down

• MODFLOW, ISIS, MIKE 11• Hydraulics modelled• Spatial data

Complex geology

• Spatial variations in strata type

• Spatial variation in permeability of rocks (hydraulic conductivity)

Great Cressingham Fen MODFLOW map

570000 572000 574000 576000 578000 580000 582000 584000 586000 588000 590000 592000 594000 596000 598000288000

290000

292000

294000

296000

298000

300000

302000

304000

306000

308000

310000

312000

314000

N orthw old

E W 23A

E W 22

EW 13

E W 12

EW 10

EW 9

EW 7A

EW 6

E W 4 EW 3 EW 1

E W 14AE W 17

E W 18

E W 19

E W 20B

E W 21

TF70/ 038

TF70/ 070

TF70/ 127

TF 80/005

T F80/006

T F80/014

TF 80/021

TF 80/ 022

TF 80/192

TF80/216T F80/217

T F80/225T F80/226

T F80/230T F80/231

TF90/ 001

TL89/ 002

TL89/ 005

TL89/ 006TL89/014T L89/ 017

T L89/019

TL99/005

TL99/ 008

TL99/017A

Groundwater data needs

Water table modelling• MODFLOW groundwater model

• water table contours

• areas of inundation

Impact Assessment of Wetlands

Stage 1 Hydrological impacts assessment (abstraction on wetland hydrology)

Stage 2 Ecological impacts assessment (hydrology on wetland biota)

Defining Thresholds/Needs

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40J F M A M J J A S O N D

Desirable

Tolerable

Unacceptable

MG13 Grassland (Midelney soil)

Month

Dep

th to

wat

er ta

ble

(cm

)

N

0 150m

Great Cressingham Fen

Great Cressingham Fen - Summary

• The ADDITIONAL shallow water table drawdown related to an increase from natural (no abstraction) to full licensed abstraction is predicted to be around 11 cm

• Given the relative sensitivity of M13 to reduced water levels, an adverse effect cannot be ruled out at this stage.

Key concepts• Conceptual

understanding• Fit for purpose• Uncertainty• Risk-based approach• Stakeholder

responsibility

http://www.uni-tuebingen.de/gracos/gif/eu.gif

EUROWET

Integration of European Wetland research in sustainable management of the water cycle

Hydrology Task Force review paper